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Swap rax and rbx to optimize machine code a bit.

This commit is contained in:
Andrius Štikonas 2022-07-23 15:15:40 +01:00
parent 7f27324a5b
commit 93c8c5372c
1 changed files with 14 additions and 13 deletions
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27
amd64/Development/hex0.S
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@ -22,6 +22,7 @@
.global _start
.text
# efi_main(void *image_handle, struct efi_system_table *system)
_start:
mov rbp, rsp # save stack pointer
mov r15, rcx # save image_handle
@ -41,31 +42,31 @@ _start:
mov r9, rcx # arg4 = image_handle
# arg1 = ImageHandle (already set)
sub esp, 32 # allocate shadow stack space for UEFI function
call r14 # system->boot->open_protocol(image_handle, &guid, &image, image_handle, 0, EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL);
call r14 # system->boot->open_protocol(image_handle, &guid, &image, image_handle, 0, EFI_OPEN_PROTOCOL_BY_HANDLE_PROTOCOL)
mov rax, [rsp+64] # get image
# Command line args
mov rcx, rax # save image
mov rax, [rax+56] # options = image->load_options
mov rbx, [rax+56] # options = image->load_options
loop_options1: # Skip application name
add rax, 2 # ++options
mov bl, [rax] # *options
cmp bl, 0x20 # if *options != ' '
add rbx, 2 # ++options
mov al, [rbx] # *options
cmp al, 0x20 # if *options != ' '
jne loop_options1 # then jump
add rax, 2 # ++options
mov r12, rax
add rbx, 2 # ++options
mov r12, rbx
loop_options2: # Skip argv[1]
add rax, 2 # ++options
mov bl, [rax] # *options
cmp bl, 0x20 # if *options != ' '
add rbx, 2 # ++options
mov al, [rbx] # *options
cmp al, 0x20 # if *options != ' '
jne loop_options2 # then jump
mov byte ptr [rax], 0 # *options = 0;
add rax, 2 # ++options
mov r13, rax
mov byte ptr [rbx], 0 # *options = 0;
add rbx, 2 # ++options
mov r13, rbx
# Get root device
push rax # allocate stack for rootfs